1. Field of the Invention
The present invention relates to an organic electroluminescent display (ELD) device, and more particularly, to an organic electroluminescent display device where a display quality is improved by preventing a light leakage.
2. Discussion of the Related Art
Although a cathode ray tube (CRT) was widely used as a display device, a flat panel display (FPD) such as a plasma display panel (PDP) device, a liquid crystal display (LCD) device and an organic electroluminescent display (ELD) device, which may be referred to as an organic light emitting diode (OLED) device, has been the subject of recent research and development.
Among various FPD devices, organic ELD devices of an emissive type have advantages of a light weight and a thin profile due to omission of a backlight unit. In addition, organic ELD devices have a viewing angle and a contrast ratio superior to LCD devices, and have advantages in a power consumption such that organic ELD devices are driven with a low direct current (DC) voltage. Further, organic ELD devices have a fast response speed, an excellent durability against an external impact and a wide operation temperature range. Specifically, since the fabrication process for organic ELD devices is simple, organic ELD devices have a lower production cost as compared with LCD devices.
Organic ELD devices may be classified into a passive matrix type and an active matrix type according to existence of a switching element. In passive matrix type organic ELD devices, a scan line and a signal line crossing each other to define a pixel region are disposed in a matrix without a switching element. In active matrix type organic ELD devices, a scan line and a signal line crossing each other to define a pixel region are disposed in a matrix and a thin film transistor (TFT) as a switching element and a storage capacitor are disposed in each pixel region.
Since passive matrix type organic ELD devices have disadvantages in resolution, power consumption and lifetime, active matrix type organic ELD devices having advantages of high resolution and large size have been the subject of recent research and development.
FIG. 1 is a cross-sectional view showing an active matrix type organic electroluminescent display panel according to the related art. In FIG. 1, an organic electroluminescent display (ELD) device 10 includes first and second substrates 1 and 2 facing and spaced apart from each other, and the first and second substrates 1 and 2 are attached to each other with a seal pattern 20 at an edge portion of the first and second substrates 1 and 2. The first substrate 1 includes an active area AA for displaying images and a non-active area NA surrounding the active area AA.
A driving thin film transistor (TFT) DTr is formed on the first substrate 1 in the active area. In addition, a first electrode 11, an organic luminescent layer 13 and a second electrode 15 constituting an organic electroluminescent (EL) diode E are sequentially formed on the first substrate 1. The first electrode 11 is electrically connected to the driving TFT DTr. The first and second electrodes 11 and 15 may function as an anode and a cathode, respectively. The organic luminescent layer 13 includes red, green and blue organic luminescent patterns 13a, 13b and 13c in each pixel region.
When the organic ELD device 10 has a bottom emission type, the first electrode 11 may be formed of a transparent conductive material and the second electrode 15 may be formed of a conductive material so that light from the organic luminescent layer 13 can be emitted through the first electrode 11. The second substrate 2 includes a groove 40 and an absorbent material 30 is formed in the groove 40 to eliminate moisture penetrated from exterior.
The groove 40 is formed by etching the second substrate 2 using a mask. The groove 40 has a rectangular shape and corner portions of the rectangular shape may have residues due to incomplete etching.
FIG. 2A is a cross-sectional view showing a light leakage at a corner portion of an organic electroluminescent display device according to the related art, and FIG. 2B is a plan view showing residues in a second substrate for an organic electroluminescent display device according to the related art. In FIGS. 2A and 2B, a first substrate having a driving TFT DTr and an organic EL diode E is attached to a second substrate 2 with a seal pattern 20. The second substrate 2 includes a groove 40 and an absorbent material 30 is formed in the groove 40. The groove 40 has a rectangular shape and has a first depth t1 from an inner surface of second substrate 2.
The groove 40 may be formed by etching the second substrate 2 using a mask, and residues 40a may be formed at corner portions of the groove 40 due to a slower flow of an etching source. Accordingly, a sidewall and a bottom surface of the groove 40 form a right angle in a side portion except the corner portions, while the sidewall and the bottom surface of the groove 40 form a rounded angle due to the residues 40a in the corner portions. Each residue 40a may have sides each corresponding to the first depth t1 from the corner point.
The residues 40a cause a light leakage, and display quality such as brightness and color uniformity of the organic ELD device 10 is degraded due to the light leakage. The light from the organic luminescent layer 13 may be emitted to the residues 40a through the second electrode 15. In addition, the light is reflected and refracted at the residues 40a, and is transmitted to the first substrate 1. As a result, the light through the second electrode 15, which is undesired light, is emitted from the organic ELD device 10 to form the light leakage.